Micro-electromechanical semiconductor component and method for the production thereof

ABSTRACT

The micro-electromechanical semiconductor component is provided with a first semiconductor substrate, which has an upper face, and a second semiconductor substrate, which has an upper face. Both semiconductor substrates are bonded resting on the upper faces thereof. A cavity is introduced into the upper face of at least one of the two semiconductor substrates. The cavity is defined by lateral walls and opposing top and bottom walls, which are formed by the two semiconductor substrates. The top or the bottom wall acts as a reversibly deformable membrane and an opening extending through the respective semiconductor substrate is arranged in the other of said two walls of the cavity.

The invention relates to a micro-electromechanical semiconductorcomponent and a method for producing the same. Particularly, theinvention relates to a micromechanical component being compatible withregard to usual semiconductor component manufacturing processes andhaving a low power consumption, and particularly a micromechanical CMOSsensor having a reversibly deformable membrane for receiving pressureforces and other forces.

The design of micro-electromechanical and respectively micromechanicalcomponents made of semiconductor material for application as pressureand respectively acceleration sensors is basically known. Thesemicro-electromechanical semiconductor components comprise a cavity whichis covered by a reversibly deformable membrane. Herein, one mostly usestwo semiconductor substrates (the so-called handle wafer and theso-called device wafer) which are mutually bonded on top of each other.In at least one of the two semiconductor substrates, a cavity has beenformed beforehand by an etching process, said cavity being then coveredby the other semiconductor substrate. The cavity is also referred to asa “buried cavity”.

In the above described manner, absolute pressure sensors can be producedin a quite reliable manner.

It is an object of the invention to produce differential pressuresensors by use of the buried cavity technology.

For achieving the above object, there is proposed, according to theinvention, a micro-electromechanical semiconductor component comprising

-   -   a first semiconductor substrate having an upper face,    -   a second semiconductor substrate having an upper face,    -   both semiconductor substrates being bonded resting on the upper        faces thereof,    -   a cavity being introduced into the upper face of at least one of        the two semiconductor substrates, and    -   said cavity being defined by lateral walls and opposing top and        bottom walls which are formed by the two semiconductor        substrates, and    -   the top or the bottom wall acting as a reversibly deformable        membrane, and an opening extending through the respective        semiconductor substrate being arranged in the other of said two        walls of the cavity.

For achieving the above object, there further serves a method forproducing a micro-electromechanical semiconductor component, comprisingthe following steps:

-   -   providing a first semiconductor substrate having an upper face,    -   providing a second semiconductor substrate having an upper face,    -   forming a cavity in the upper face of at least one of the two        semiconductor substrates,    -   bonding the two semiconductor substrates resting on each other        by their upper faces,    -   etching, into one of the two semiconductor substrates, an        opening entering said cavity.

A method for producing a micro-electromechanical semiconductorcomponent, comprising the following steps:

-   -   providing a first semiconductor substrate (1) having an upper        face,    -   providing a second semiconductor substrate (5) having an upper        face,    -   forming a cavity (4) in the upper face of at least one of the        two semiconductor substrates (1,5),    -   bonding the two semiconductor substrates (1,5) resting on each        other by their upper faces,    -   etching, into one of the two semiconductor substrates (1,5), an        opening (98) entering said cavity (4).

The invention thus provides a micro-electromechanical semiconductorcomponent which can be used as a differential pressure sensor, wherein,for producing this sensor, use is made of the known and well-provenburied cavity technology. Up to now, for producingmicro-electromechanical differential pressure sensors, their cavitiesand membranes were etched free from the rear side. In themicro-electromechanical semiconductor component of the invention, bygenerating an etched opening which enters the cavity, the semiconductormaterial delimiting the cavity will be maintained; into thissemiconductor material, there will instead be etched only thesmall-sized opening which is situated in the otherwise completelymaintained bottom wall of the cavity arranged opposite to the membrane.Thus, the micro-electromechanical semiconductor component of theinvention has an increased robustness against housing and assemblystress. The torsional stiffness of the micro-electromechanicalsemiconductor component of the invention is guaranteed, as in the designof absolute pressure sensors, by the buried cavity technology throughthe mutually bonded semiconductor substrates; nonetheless, themicro-electromechanical semiconductor component of the invention can beused as a differential pressure sensor.

Suitably, the cavity is generated by forming it only in one of the twosemiconductor substrates, the other semiconductor substrate thenserving, after bonding, for covering and closing the cavity. In thisarrangement, the cavity is defined by surrounding side walls formed inone or both semiconductor substrates, and by opposing top and bottomwalls. One of the two latter walls acts as reversibly deformablemembrane while the etched opening is formed in the other wall which isarranged opposite to this membrane. The opening will be suitablygenerated in the last method step by a wet or dry chemical process.Prior to that, e.g. by a common component production process (e.g. CMOSprocess), electric and/or electronic components have been produced in atleast one of the two semiconductor substrates. Further, at this priortime, if required, the membrane has been at least partially be reducedin thickness, which has been performed e.g. by trenches formed in themembrane by etching or by similar depressions serving for thinning thematerial.

The invention will be explained in greater detail hereunder withreference to the drawing. Specifically, the drawings show the following:

FIG. 1 Process for producing a structure in accordance with theinvention:

-   -   a) raw wafer    -   b) oxidation and opening of windows    -   c) etching the cavity    -   d) bonding the top wafer (followed by the CMOS process, which is        not especially shown)    -   e) etching the trenches (after the CMOS process).

FIG. 2 Three-dimensional simplified sectional view of a pressure sensorproduced according to the process of FIG. 1.

FIG. 3 Alternative second process for producing a structure inaccordance with the invention:

-   -   a) raw wafer    -   b) oxidation and opening of windows    -   c) etching the cavity    -   d) bonding the handle wafer (followed by the CMOS process on the        top wafer with cavity, which is not especially shown)    -   e) etching the trenches (after the CMOS process).

FIG. 4 Three-dimensional simplified sectional view of a pressure sensorproduced according to the process of FIG. 3.

FIGS. 5 to 10

-   -   Alternative third process for producing a structure in        accordance with the invention:    -   a) raw wafer    -   b) oxidation    -   c) application of polysilicon layer and partial oxidation    -   d) second raw wafer    -   e) oxidation and opening of a window    -   f) etching the cavity    -   g) bonding the handle wafer    -   h) partial grinding (followed by the CMOS process on the top        wafer with cavity, which is not especially shown)    -   i) etching the trenches (after the CMOS process)    -   j) three-dimensional simplified sectional view of a pressure        sensor produced according to the process of FIGS. 5 to 9.

FIG. 11 Example of the layout of a transistor.

FIG. 12 Connection of four transistors to form a Wheatstone bridge(operation of the transistors as resistors).

FIG. 13 Exemplary connection of four transistors and two furthertransistors to form a Wheatstone bridge with reference voltage source.

FIG. 14 Exemplary layout of a Wheatstone bridge.

FIG. 15 Connection of eight transistors to form a Wheatstone bridge,with a second short-circuited Wheatstone bridge as a reference voltagesource.

FIG. 16 Example of a placement of four Wheatstone bridges according toFIG. 12 on a sensor die with trench structure.

FIG. 17 Example of a placement of four Wheatstone bridges with fourWheatstone bridges as stress-free references according to FIG. 15 on asensor die with trench structure (For better survey, the voltagereferences are not illustrated. In principle, for each pair ofWheatstone bridges, there will suffice a third, short-circuitedWheatstone bridge besides the stress-free reference bridge. Thus, 12Wheatstone bridges would be found on the die).

FIG. 18 Exemplary layout of a differential stage.

FIG. 19 Exemplary circuit arrangement for a circuit with a differentialamplifier and a referential differential amplifier as a referencevoltage source.

FIG. 20 View onto an exemplary membrane geometry with quadratic trenchsystem

-   -   a) plan view    -   b) view from below.

FIG. 21 View onto an exemplary membrane geometry with quadratic trenchsystem and rhombic central portion

-   -   a) plan view    -   b) view from below.

FIG. 22 View onto an exemplary membrane geometry with quadratic trenchsystem which was chamfered in the corners, and with rhombic centralportion

-   -   a) plan view    -   b) view from below.

FIG. 23 View onto an exemplary membrane geometry with quadratic trenchsystem and webs in the corners,

-   -   a) plan view    -   b) view from below.

FIG. 24 View onto an exemplary membrane geometry with round trenchsystem and round cavity,

-   -   a) plan view    -   b) view from below.

FIG. 25 View onto an exemplary membrane geometry with round trenchsystem and non-continuous webs,

-   -   a) plan view    -   b) view from below.

FIGS. 26 and 27

-   -   sensors with additional trenches.

FIG. 28 Boss (central membrane reinforcement) with mass reduction byetched support structure 97.

FIGS. 29 and 30

-   -   Exemplary differential pressure sensors generated from the above        sensors by etching an opening 119.

FIG. 31 View onto an exemplary membrane geometry with round cavity,round outer edge of the trench system, and rhombic central portion

-   -   a) plan view    -   b) view from below.

FIG. 32 View onto an exemplary membrane geometry with round cavity,round outer edge of the trench system, and rhombic central portion, andadditional trenches for protection of the system against spreading ofexternally introduced stress

-   -   a) plan view    -   b) view from below.

FIG. 33 Circuit diagram of a bridge according to FIG. 34 and FIG. 35 asa measurement bridge with reference voltage source.

FIG. 34 Exemplary layout of a measurement bridge with common gate.

FIG. 35 Further exemplary layout of a measurement bridge with commongate.

FIG. 36 Equivalent circuit diagram of a transistor according to FIG. 37as a measurement bridge with reference voltage source.

FIG. 37 Exemplary layout of a particularly small measurement bridgetransistor with four connectors.

FIG. 38 A detailed view.

FIG. 39 A schematic view illustrating the individual method steps forpreparing and for bonding two semiconductor substrates for producing adifferential pressure sensor with buried cavity technology.

FIG. 40 A view of the absolute pressure sensor produced with the aid ofthe buried cavity technology.

FIG. 41 A view of the sensor according to FIG. 40, but, by generating anetched opening entering the cavity, now in its design as a differentialpressure sensor.

FIGS. 42 to 44

-   -   Views of alternative process steps for producing a differential        pressure sensor with buried cavity technology.

The invention will be illustrated by way of example of a pressure sensorfor detection of low pressures. A first essential aspect of theinvention resides in the generating of the pressure sensor cavity 4prior to the processing of the CMOS steps. Thereby, random standard CMOSprocesses can be performed on the surface. This makes it possible, as asecond essential step, to place CMOS transistors on a membrane in such amanner that they will lie in a region of optimal mechanical stress upondeflection of the membrane. This point can be determined by analyticconsiderations and/or finite element simulations.

A first exemplary process is represented, by way of essential stepsthereof, in FIGS. 1 and 2. Modifications of this first process will bedescribed further below.

The basic manufacturing process starts with a first wafer 1 whichpreferably consists of the same material as a later used second wafer 5.On this wafer, a layer 2 is deposited which serves for later connection.In silicon wafers, this layer will be formed as a SiO₂ layer 2 byoxidation. Within this layer, a window will be opened and the laterpressure sensor cavity 4 will be etched (FIG. 1 c). Said etching ispreferably performed by a DRIE or plasma etching step becauseparticularly the first one will result in straight walls 3.

The upper wafer 5 will likewise be provided with an oxide layer and willbe bonded onto the first wafer 1 and be ground (FIG. 1 d). The bondingprocess herein is preferably performed in a vacuum. This will lead to acavity which is not filled with gas, and will prevent a latertemperature dependence of the interior pressure in the cavity. By thisprocess, a membrane is generated in the region of the cavity, whosethickness is determined by the grinding process.

As a result, one will obtain a wafer package which can be used in astandard CMOS process or standard bipolar process in the same way as anormal SOI material.

After the CMOS processing, which does not have to be described ingreater detail here because the processing can be gathered from standardliterature, further micromechanical structures 6 can then be etched intothe surface 11 (FIG. 1 e).

In the case of the exemplary pressure sensor, these micromechanicalstructures 6 are e.g. trench structures forming approximately closedrings or quadrangles which are interrupted only by few webs 8 (FIG. 2).In the middle, there is thus generated a central plate 12—referred to asa boss—which, due to the increased thickness, forms a reinforcement. Thebottom of the trenches 6 forms a membrane 7 of reduced thickness. Thismembrane typically takes up substantially less forces. It is importantherein that the outer edge of the trench 6 is sufficiently spaced fromthe wall of the cavity 3 since, otherwise, small adjustment errors inmanufacture would have a massive effect on the mechanical stress andthus on the measurement result. This is a substantial innovation. Thereproducibility, under the aspect of production technology, of thesensor properties, would otherwise suffer, which would cause increasedexpenditure for calibration and therefore would entail correspondingcosts.

Thus, the pressure on the central plate 12 is dissipated virtuallyexclusively through mechanical tension via the webs 8. Consequently, itis reasonable to place onto said webs those components 9 which aresensitive to mechanical stress and are provided to detect this stress.These are connected to the connectors 10 via lines. Thus, by thetrenches, the mechanical stress field will be adjusted relative to thestress-sensitive electronic components.

By way of alternative, the cavity can also be etched into the upperwafer. This is correspondingly represented in FIGS. 3 and 4 in steps ato f.

An essential disadvantage of the two above processes is the absence of anatural etching stopper for the etching of the trenches 6. For thisreason, the thickness of the membrane at the bottom of the trenches 7can be controlled only with difficulty. As a consequence, the relativeerror is comparatively high, causing a dispersion of the sensorparameters.

A third exemplary process which is free of the above disadvantage isrepresented, by way of essential steps thereof, in FIGS. 5 to 10 andsteps a to j.

The manufacturing process starts with a first wafer 13 which preferablyis of the same material as the later used second wafer 16. Onto thiswafer, there is applied a connection layer which in the case of siliconwafers is a SiO₂ layer 14. On this SiO₂ layer, a further layer will bedeposited, e.g. a polysilicon layer or amorphous silicon layer 15, andwill be superficially oxidized (FIG. 5 c). The depositing of this layertypically can be controlled very well and thus will be considerably moreprecise in its result than the etching of the trenches in the first twodescribed processes. The second wafer will be oxidized as well, thuslikewise generating an oxide layer 17. In this layer, at least onewindow will be opened and the later cavity 18 will be etched. Saidetching is preferably performed by a DRIE etching step because this stepwill result in straight walls (FIG. 6 f). It is of course also possibleto etch the cavity 18 into the upper wafer 13, but this will not bedescribed in greater detail hereunder.

The upper first wafer 13 will be bonded onto the second wafer 16 (FIG.7) and subsequently will be grinded (FIG. 8). The bonding process hereinwill preferably again be performed in a vacuum so as to exclude a latertemperature dependency of the interior pressure in the cavity 18. Bythis process, a membrane is generated in the region of cavit, whosethickness is determined by the grinding process.

As a result, one will again obtain a wafer package which in principlecan be used in a standard CMOS process or standard bipolar process inthe same way as a standard wafer.

After the CMOS or bipolar processing, further micromechanicalstructures, e.g. trenches 19, can then be etched into the surface 24(FIG. 10) as in the above describes processes.

In the case of a pressure sensor, these micromechanical structures 19are again e.g. trench structures forming approximately closed rings orquadrangles which are interrupted only by few webs 20. In the middle,there is thus again generated a central plate 21 which, due to theincreased thickness, forms a reinforcement. The bottom of the trenches19 forms a membrane 25 of reduced thickness. This membrane typicallytakes up virtually no forces. In contrast to the first method, theadditional layer 15 and the resultant additional oxide layer 14 make itpossible to stop the etching of the trenches 19 with greater precisionthan in the first method. Thereby, the electromechanical properties canbe realized more precisely and with better repetitive accuracy.

As in the result of the first process, the pressure (see FIG. 10) on thecentral plate 21 is dissipated virtually exclusively via the webs 20.Consequently, it is again reasonable to place onto said webs thosecomponents 22 which are sensitive to mechanical stress and are providedto detect this stress. These are connected to the connectors 22 vialines.

Of course, it can also be envisioned, instead of using a depositingprocess, to produce said additional layer 15 by bonding and grinding athird wafer. Further, it can be envisioned to integrate more than oneburied insulated layer of the type of said additional layer 15 into awafer packet.

With a wafer package generated in this manner, it is possible again toproduce stress-sensitive sensors on the membrane after their productionprior to generating the trenches (6 or 19).

To this end, in a CMOS or bipolar process, stress-sensitive electroniccomponents are produced on the respective surface 11,24 and areconnected. For a CMOS process, preferred use is made of a p-dopedsubstrate.

For instance, piezoelectric resistors can be placed on the webs 20,8 andbe connected to form a Wheatstone bridge. These, however, have thedisadvantage that they first must be brought onto the operatingtemperature and will consume relatively much electrical energy duringmeasurement. Thus, they are unsuited for energy-autonomous systems. Asalready described above, the invention also aims at eliminating thisproblem.

Thus, in place of such simple electronic components, it is reasonable touse actively amplifying components such as e.g. bipolar transistors andMOS transistors. These can again be connected to form a Wheatstonebridge but will need no warm-up time and will consume less energy. Anexemplary circuit arrangement is shown in FIG. 12.

Herein, four p-channel transistors 85,86,87,88 form a Wheatstone bridgewhich can be sensed at the two terminals 89,90. The transistors 87 and85 herein are designed with the same orientation, and also thetransistor pair 88,86 is given the same orientation but is arrangedvertically to the transistor pair 87,85. However, this circuit is highlysensitive to manufacturing faults.

Now, to make it possible to produce such a MOS transistor circuit withsufficient accuracy, the transistors have to be designed in such amanner that the electrically active part is self-adjusting. FIG. 11shows an exemplary layout of such a self-adjusting transistor. Herein,the p+-contact implantations 80 and 79 are shaded by the poly gate 81 insuch a manner that, also in case of displacement, there will always bemaintained the same transistor channel length and transistor width. Thepoly gate 81 also shades the n+-channel stopper implant. The gate isconnected via a low-impedance poly line.

Thus, it is safeguarded that the transistors of identical designgeometries have a similar geometry in their physical realization. Thisgeometry is determined substantially by the design of the polysiliconsurface.

To bring the transistors to the respective correct operating point, itis suitable to also integrate a reference voltage source on the pressuresensor. In the example (FIG. 13), the exemplary reference voltage sourceconsists of the transistors 30 and 29. The transistors 31,32,33,34 againform a Wheatstone bridge which can be sensed at the terminals 28,36.Both are connected as MOS diodes by connection of the gate to the drain.The reference voltage of transistor 30 is connected to the gate oftransistors 31 and 33. The reference voltage of transistor 29 isconnected to the gate of transistors 32 and 34. In the example of FIG.13, the drain of transistor 29 is on the potential of terminal 26. Inp-channel transistors, this terminal is typically connected to ground.Therefore, the drain contacts of transistors 32 and 34 are likewiseconnected to this terminal. The transistors are preferably realized withidentical geometric dimensions. An example of the layout of a localWheatstone MOS bridge is illustrated in FIG. 14. If the transistors arearranged as in FIG. 14, the transistors 31 and 34 are orientedidentically. The transistors 23 and 33 are also oriented identicallyrelative to each other but vertically to transistors 31 and 34. FIG. 14shows an exemplary arrangement.

To keep the mechanical distortion on the membrane at a minimum, themembrane is not provided with a field oxide but only with afull-surfaced, extremely thin gate oxide of a few nm and a suitablepassivation. If the application of a field oxide is unavoidable, highsymmetry is recommendable so as to keep parasitic effects on allstress-sensitive components at an identical level. In a silicon pressuresensor, for instance, the passivation can consist of silicon nitride.This has a low hydrogen diffusion coefficient and thus will protect thecomponent against in- and out-diffusion of protons which, particularlyin case of a permanently applied voltage and a high operatingtemperature may cause a drift of the p-resistors and the p-channeltransistors. This effect is known as NBTI. In order to avoid anypossible kind of mechanical distortion, no field oxide or the like willbe generated near mechanical components or even on these. Therefore,particularly the membrane of the exemplary pressure sensor is coveredonly with the gate oxide and the passivation layer, silicon nitride.Further, the feed lines on the die will be realized, if possible, not inmetal, which has a high thermal expansion coefficient particularlyrelative to silicon, but in the wafer material and, in case of silicon,as a high-doped layer or as a high-doped polysilicon or, if not possibleotherwise, as a high-doped amorphous or polycrystalline silicon. In thisexample (FIG. 14), the drain and source feed lines of the transistors26,28,35,36 are realized e.g. as p+-implants 36,35,26, 28. The gates andtheir feed lines are realized e.g. in polysilicon 33,39,31 and 32,34,38.In the surface 40 which will be n-doped, no channel will be formed inthis example, which is due to the field threshold. This will be possibleonly at the edge of the poly gates. For this reason, there is implanteda n+-channel stopper 37 which will interrupt parasitic forces. By thisexemplary all-silicon realization, it is thus possible that the elementsensitive to mechanical stress can be kept very small and insensitive tomanufacturing tolerances and thermomechanical stress caused by foreignmaterials, so that the sensitivity to inhomogeneous stress distributionwill be further reduced. In spite of these provisions, there still existmarginal differences between the materials. For this reason, whendesigning the electronic components on the die, and particularly incomponents arranged on the membrane, care is taken to maintain thehighest possible symmetry. Thus, it is reasonable that components whichare used for differentiation—e.g. those in Wheatstone bridges ordifferential amplifiers—are placed as closely together as possible so asto minimize the influence of manufacturing inhomogeneities.

FIG. 15 shows a further variant of the Wheatstone bridge. Therein, thereference voltage by which the bridge consisting of the transistors31,32,33, 34 is operated, is generated from a bridge similar to thatone, consisting of transistors 30,29,55,56. Suitably, herein, use ismade of the same layout module. The reference bridge will beshort-circuited, thus generating the reference voltage 35 by which thetransistors 31,32,33,34 of the first bridge are controlled. The secondbridge will be placed on the substrate as far away as possible from themechanical tensions but still as close as possible to the first bridge.This serves for keeping the manufacturing variations between the bridgesas small as possible. The first bridge will be placed at the point ofsuitable mechanical stress. This is the point where a mechanical stressas high as possible will be generated upon deflection of the exemplarymembrane while, however, this stress is still so homogenous thatmanufacturing variations will not yet be perceived too massively.

For further minimization of influences of misalignment, it can bereasonable to place a plurality of bridges on one die. This can beeffected e.g. by a placement as shown in FIG. 16. Here, there is shownthe possible placement of four bridges according to FIG. 12. FIG. 17shows the placement of bridges and reference bridges according to FIG.15. In an arrangement as shown in FIG. 17, three levels of compensationexist. On the first level, the level of the four transistors, thedirection of the mechanical stress will be detected. This is performedby comparison between values of transistors arranged mutuallyvertically. On the next level, these four transistors in their totality43 will be compared to four further, similarly arranged transistors 58located close to the first four ones, 43, but in a mechanically lessstressed region, ideally on the neutral fiber. Thereby, the mechanicallyinduced offset of the bridge will be differentiated from that offsetwhich is caused by adjustment errors during manufacture. If the sensoris symmetric, it is reasonable to install eight further transistors,according to the number of positions on the axis of symmetry. In theexample (FIG. 17), these are four pairs of sensors44,57;41,60;42,59;43,58, each pair consisting of two by fourtransistors.

Theoretically, the placement of a single transistor is alreadysufficient for stress measurement. In this case, however, allmanufacturing errors will already have a massive effect.

A first alternative layout is shown in FIG. 34. FIG. 33 shows theappertaining circuitry with a reference voltage source consisting of thetransistors 108, 109. Here, the four transistors 104,105,106,107connected to form a Wheatstone bridge have a common gate 110, whichsimplifies the layout. Via the terminals 103 and 102, the bridge issupplied with voltage. In case of a mechanical distortion of the bridge,an electric voltage will appear at the terminals 111,112. FIG. 35illustrates a further variant of this bridge. If the channel stopper 37in the middle of the bridge is omitted, this results in afield-plate-like transistor 115 with four terminals (FIG. 37). FIG. 36shows the equivalent circuit diagram of transistor 115. Added theretoare then the transistors 114 and 113 which, on the one hand, increasethe current consumption, 114, and, on the other hand, reduce the signallevel, 113. As a benefit thereof, however, the design size and thus thespace requirement can be minimized, which in some applications is veryuseful.

An alternative layout arrangement of the transistors of a sensor element41,42,43,44,57,58,59,60 is shown in FIG. 18. Here, the four transistors44,45,46,47 are arranged in a star-shaped configuration. They have acommon drain contact 50 which via a feed line 49 is connected to acurrent source that is not located on the membrane of the pressuresensor. The gates of the transistors 44,45,46,47 are connected by a polyline 48. The source contacts are respectively connected by a highlydoped p+-conduit 51,52,53,54. The four transistors are e.g. componentsof a differential amplifier as shown in FIG. 19. All other transistorsof FIG. 19 are not arranged on the membrane but on the substrate withoutunderlying cavity. It is obvious that already half of the fourtransistors, i.e. for instance the transistors 45 and 44, would besufficient to form a differential amplifier. For reasons of symmetry,however, the variant comprising four transistors is recommendable.

The circuit consists of two differential amplifiers. The left-handamplifier (transistors 65 to 73) is short-circuited in the output andthe input and operates as a reference voltage source for the operationof the second amplifier. These transistors are arranged in a regionwhich is free of mechanical stress. The above described transistors44,45,46,47 form the differential stage with the respective appertaining“working resistors” 61,62,63, 64. The current source 74 supplies currentto the thus formed differential amplifier. The transistor 74 in thisexample is an n-channel transistor. In operation, the outputs of thedifferential amplifier 77,78 will reflect an asymmetry of thetransistors 44,45,46,47 due to mechanical stress. Since the transistors46 and 44 are oriented differently from the transistors 45 and 47, auniaxial mechanical stress will result in an output signal at 77,78. Thedifferential amplifier in this example will be brought to the workingpoint by a similarly designed, short-circuited reference differentialamplifier. The latter and the transistors 61,62,63,64,74 are suitablyarranged not on the membrane but in a region of the die which is nearlyfree of mechanical stress. In order to guarantee the congruence of theelectrical parameters of the components in the stress-free state, theseshould nonetheless be placed as close to the other transistors aspossible. Thus, the orientation and the layout of all elements suitablywill be realized as closely adjacent as possible and with the sameorientation so that particularly also the current-mirror pairs will bewell attuned to each other.

FIGS. 20 to 25 show different embodiments of the trenches and cavities.

In the design of the race track 6 and the cavity 3, various factors haveto be considered:

-   1. A suitable distance has to be maintained between the race-track    outer wall and the cavity wall.-   2. The circle passing through the outer contact points of the webs    with the race-track outer wall is not to be intersected by the    race-track outer wall because this would result in a distortion of    the mechanical stress field in the boss 12.-   3. The connecting lines between the base points of the webs 8 on    boss 12 is not to be intersected by the outer edge of the boss    because this would result in a distortion of the mechanical stress    field in the boss.-   4. The construction should, if possible, comprise no corners because    very strong voltages could occur in these, causing nonlinear effects    and bi-stability.

Opposed to the above demands are demands with regard to the burstpressure. If the race-track surface becomes too large, the race-trackmembrane will break more quickly.

To decouple the membrane from mechanical stress caused by the design aand the connection technology, it is thus reasonable e.g. to generate afurther trench 93 around the sensor (FIG. 26) and in this manner togenerate a virtually larger race-track membrane without the abovementioned danger of breakage.

Herein, the sensor is suspended on webs 94. In the ideal case, these areno extensions of the webs 8 on which the boss 12 is fastened. Thereby,mechanical stress will be transmitted to the sensors 9 only indirectlyfrom outside.

This principle can still be continued by a further trench 95 and furtherwebs 96 (FIG. 27).

The construction with the aid of a boss will lead to an increasedsensitivity to seismic stresses. This sensitivity can be lowered byreducing the boss mass (FIG. 28). For this purpose, a suitable supportstructure will be etched into the boss 97. There will remain webs which,if suitably selected, will generate a sufficient areal moment of inertiafor guaranteeing the mechanical stability. The sensor 22 herein will beplaced, as above, on a web 20 interrupting the race-track trench 19.

In case that, instead of an absolute pressure sensor, a differentialpressure sensor is to be generated, this can be performed by subsequentetching of an opening 119 into the lower wafer. FIGS. 29 and 30 showcorresponding exemplary shapes. The advantage of such a constructionresides in the small opening and thus in the only very small loss ofstability in comparison to a sensor wherein the cavity was etched fromthe rear side.

The bonding system normally is made of metal having a considerablydeviating thermal expansion coefficient. Further, the metal will causehysteresis effects. Thus, it is reasonable to decouple the bond pads 10from the rest of the sensors as far as possible. This can be effected bymechanical guard rings in the form of trenches 157 which e.g. will belaid as far as possible around the pads or to-be-protected parts (FIG.32).

Hereunder, with reference to FIGS. 39 to 43, alternative productionmethods for generating a differential pressure sensor of the inventionas configured by buried cavity technology will be discussed again. Inthis context, it is to be pointed out that the details shown in FIGS. 39to 43 are to be understood e.g. as described further above.

According to FIG. 39, there is first applied, onto a handle wafer 1(first semiconductor substrate—see FIG. 39 a), an oxide layer 2 (seeFIG. 39 b) into which a window (see again FIG. 39 b) will be etched byphotolithography. Then, by use of an etching process (e.g. DRIE or KOH)a cavity 4 will formed in the semiconductor substrate 1. Through thetype of the etching process used, the slant or inclination of the sidewall of the cavity can be defined. For instance, a DRIE etching processwill generate nearly vertical side walls 3.

Onto the thus prepared handle wafer (see FIG. 39 c), a second wafer, thedevice wafer 5 (also referred to as the second semiconductorsubstrate—see FIG. 39 d), will be bonded (see FIG. 39 e). This devicewafer 5 will then be subjected e.g. to a conventional CMOS process so torealize electronic components 9 (see FIG. 40) and the wiring 11 as wellas connector pads 10. If desired or necessary, the mechanical propertiesof the membrane 7 which in this embodiment is formed by the region ofdevice wafer 5 covering the cavity 4, can be changed in a well-aimedmanner with the aid of trenches 6 and webs 8 (see FIGS. 39 f and 40).

After an absolute pressure sensor has been formed in the above describedmanner by the buried cavity technology (see FIG. 40), there will now begenerated, by a further etching step, an opening 98 entering the cavity4 and serving as a microfluidic feed line making it possible to vent thecavity 4 from the rear side of the sensor (see FIG. 41). Thus, thesensor will work as a differential sensor. In FIG. 41, it can be clearlyrecognized that the assembly of the bonded handle and device wafers willremain torsionally resistant because the cavity 4 is on all sidesdelimited by walls, while only the bottom wall is provided with theetched opening 98 which, however, has no influence on the torsionalstiffness and the areal moment of inertia of the pressure sensor. Forthe invention, it is further of essence that the etching process for theopening 98 is the final production step of the pressure sensor accordingto FIG. 41. This will only be followed, at the most, by assembling andpackaging.

FIGS. 42 to 44 illustrate alternative process steps and an alternativedesign of a pressure sensor, wherein the sole difference from theprocess and the pressure sensor of FIGS. 39 to 41 resides in that, inFIGS. 42 to 44, the cavity 4 is formed in the device wafer 5.

The invention according to FIGS. 39 to 44 has the following advantages:

-   1. Use of the buried cavity technology for the manufacture of    differential pressure sensors.-   2. Especially favorable areal moments of inertia as compared to    known differential pressure sensors whose cavity and membrane are    etched from the rear. Resultant increase of robustness against    housing and assembly stress.-   3. Reduced volume to be etched away (i.e. only the volume for the    opening 98) and resultant reduction of production costs.-   4. Possibility of cubic differential pressure sensors and thus no    necessity to bond a glass wafer below the sensor.

Further properties of the invention and of an exemplary application canbe described as follows:

-   1. A photolithographically produced transistor on a doped substrate    or in a doped trench, wherein    -   i. the transistor is electrically connected only with materials        which have a thermal expansion coefficient similar to that of        the substrate or the trench in which it is placed,    -   ii. the transistor is in no or only a very slight mechanical        connection to other materials, particularly materials having        mechanical properties different from those of the substrate or        the trench—herein, particularly field oxides,    -   iii. the transistor comprises symmetries,    -   iv. the transistor is produced in different process steps by        lithography of different geometric, mutually attuned structures,        and    -   v. these geometric structures whose superposition and        cooperation in the production process will result in the        transistor, are selected in such a manner that process        variations within the process specification limits which cause        changes of the geometries of the individual lithography step        results in the form of produced geometric structures, will have        no or only a very slight effect on the mechanical properties of        the transistors.-   2. The transistor according to item 1, which is a MOS transistor.-   3. A MOS transistor for detection of mechanical stress, comprising    four channel terminals.-   4. The MOS transistor according to item 3, which has a four-fold    rotational symmetry and a gate plate with exactly this symmetry and    channel terminals in an arrangement with exactly this symmetry,    without the need of a symmetry of the terminals of this gate plate.-   5. The transistor according to item 1, which is a bipolar    transistor.-   6. The transistor according to any one of items 1 to 4, comprising a    channel stopper.-   7. The transistor according to any one of items 1 to 4, of which the    source and/or drain regions are electrically connected by a highly    doped region or a low-impedance polysilicon.-   8. The transistor according to any one of items 1 to 7, which is    used for detection of mechanical stress.-   9. The transistor according to any one of items 1 to 8, which is    used in the manner of an electric resistor particularly in a    measurement bridge.-   10. The transistor according to any one of items 1 to 9, which is a    pnp-transistor.-   11. The transistor according to any one of items 1 to 9, which is a    npn-transistor.-   12. The transistor according to any one of items 1 to 9, which is a    p-channel transistor.-   13. The transistor according to any one of items 1 to 9, which is an    n-channel transistor.-   14. An electronic circuit comprising transistors according to one or    a plurality of items 1 to 13.-   15. An electronic circuit being in a functional relationship to a    micro-mechanical device according to item 41.-   16. The circuit according to item 14 or 15, comprising discrete    and/or integrated electronic components.-   17. The circuit according to any one of items 14 to 16, which is at    least partially produced by monolithic integration.-   18. The circuit according to any one of items 14 to 17, comprising    at least two geometrically identically designed transistors    according to any one of items 1 to 13.-   19. The circuit according to item 18, which generates a signal    suited for measurement of a different state in at least one physical    parameter of the two transistors.-   20. The circuit according to item 19, wherein said physical    parameter is mechanical stress and/or temperature.-   21. The circuit according to any one of items 18 to 20, wherein at    least two of the transistors according to any one of items 1 to 13,    irrespective of the connecting lines, are arranged symmetrically to    each other.-   22. The circuit according to any one of items 18 to 20, wherein, for    at least two of the transistors according to one or a plurality of    items 1 to 13, it is provided that their geometries, irrespective of    the connecting lines, can be brought into mutual congruence through    rotation by 90°.-   23. The circuit according to any one of items 14 to 22, comprising    at least four transistors according to any one of items 1 to 13.-   24. The circuit according to item 23, wherein said four transistors    are connected to form a measurement bridge.-   25. The circuit according to item 24, wherein the gate and source of    at least one transistor according to any one of items 1 to 13 are    short-circuited.-   26. The circuit according to item 24 or 25, wherein the gate of at    least one transistor according to any one of items 1 to 13 is    connected to a reference voltage source.-   27. The circuit according to item 26, wherein said reference voltage    source is a second, but short-circuited measurement bridge according    to any one of items 24 to 27.-   28. The circuit according to item 27, wherein said second    measurement bridge is similar to the first measurement bridge,    particularly regarding the dimensioning of the transistors and/or    the circuitry and/or the produced geometries, and/or in the extreme    case is a geometric copy of the first measurement bridge.-   29. The circuit according to any one of items 14 to 28, wherein    respectively two of said four transistors are identically oriented    while having the same geometry.-   30. The circuit according to item 29, wherein the transistors of one    transistor pair are oriented vertically to the transistors of the    other transistor pair.-   31. The circuit according to item 30, wherein said four transistors    are arranged symmetrically in a quadrangle.-   32. The circuit according to item 30, wherein said four transistors    are arranged symmetrically in a cross configuration.-   33. The circuit according to any one of items 14 to 23 or 29 to 32,    comprising at least one differential amplifier circuit.-   34. The circuit according to item 33, wherein at least one of the    transistors of at least one differential amplifier is a transistor    according to any one of items 1 to 13.-   35. The circuit according to item 33 or 34, comprising at least one    reference voltage source which is coupled to at least one first    differential amplifier.-   36. The circuit according to item 35, wherein said reference voltage    source is a second, but short-circuited differential amplifier which    is a differential amplifier according to any one of items 33 to 35.-   37. The circuit according to item 36, wherein said second    differential amplifier is similar to the first differential    amplifier, particularly regarding the dimensioning of the    transistors and/or the connection of the transistors and/or the    produced geometries of the transistors, and/or in the extreme case    is a geometric copy of the first differential amplifier.-   38. The circuit according to any one of items 14 to 37, wherein at    least a part of the circuit is also a part of the micromechanical    device.-   39. The circuit according to item 38, wherein at least a part of the    circuit is functionally connected to at least one micromechanical    functional element in such a manner that at least one mechanical    parameter of at least one micromechanical functional element is    coupled to the state function of the circuit or to at least one    electrical parameter of the state function of at least one circuit    portion.-   40. The circuit according to item 39, wherein said functional    element is particularly a bar or web, a membrane, a resonator, a lip    clamped on one side, both sides or three sides, a shield or a    needle.-   41. A micromechanical device which has been produced by lithographic    processes and by connecting, particularly bonding, at least two    wafers, wherein    -   I. prior to the connecting of said at least two wafers, at least        one micromechanical functional element in the form of at least        one surface structure has been applied on at least one surface        of at least one of said two wafers, and    -   II. after the connecting of the wafers, at least one of the thus        produced micromechanical functional elements and respectively        surface structures is situated near the boundary surface between        the wafers within the resultant wafer package, and    -   III. subsequent to the connecting of the wafers, there has been        performed, on at least one surface of the resultant wafer        package, at least one process for producing of at least one        electronic component, and    -   IV. at least one of the thus produced electronic components is        sensitive to at least one non-electric physical value and is        provided to detect the same, and    -   V. said component is produced to be self-adjusting.-   42. The micromechanical device according to item 41, wherein at    least one of said self-adjusting components is a transistor    according to any one of items 1 to 10 or is a part of the circuit    according to any one of items 14 to 40.-   43. The micromechanical device according to items 41 or 42, which is    produced from silicon.-   44. The micromechanical device according to any one of items 41 to    43, wherein said at least one micromechanical functional element is    at least one cavity.-   45. The micromechanical device according to item 44, wherein at    least one cavity together with at least one surface of the wafer    package defines a membrane.-   46. The micromechanical device according to items 44 and 45, wherein    at least one cavity comprises no oxides on its walls.-   47. The micromechanical device according to any one of items 41 to    46, wherein at least one micromechanical functional element is    situated on the surface of the device.-   48. The micromechanical device according to item 47, wherein said at    least one micromechanical functional element is a web, a trench, a    membrane, a perforation and a buried cavity or a blind hole.-   49. The micromechanical device according to item 38, wherein at    least one micromechanical functional element has been produced on    the surface after performing a process, particularly a CMOS process,    for producing a transistor according to any one of items 1 to 13 or    a circuit according to any one of items 14 to 40.-   50. The micromechanical device according to any one of items 41 to    49, wherein at least one micromechanical functional element has been    produced inter alia by use of DRIE or plasma etching processes.-   51. The micromechanical device according to any one of items 41 to    50, which can be used as a pressure sensor.-   52. The micromechanical device according to any one of items 44 to    51, wherein the geometric shape of at least one cavity comprises    symmetries with respect to the connection plane of the wafers.-   53. The micromechanical device according to any one of items 41 to    52, wherein, on at least one surface of the wafer package, the    trenches have been generated by DRIE or plasma etching.-   54. The micromechanical device according to item 53, wherein at    least one partial quantity of the trenches form a closed structure,    e.g. a ring, an ellipse, a quadrangle, a star or the like which only    at few sites are interrupted by thin webs 8,20.-   55. The micromechanical device according to items 53 and 54, wherein    at least a part of the trenches are arranged symmetrically relative    to each other.-   56. The micromechanical device according to items 52 and 55, wherein    the axes of symmetry of a part of the trenches and of at least one    cavity coincide and respectively coincide in case of an ideal    arrangement.-   57. The micromechanical device according to items 52, 55 and 56,    wherein at least a part of the trenches are in a mechanical    functional relationship with at least one cavity.-   58. The micromechanical device according to item 57, wherein the    bottom of at least one of the trenches together with at least one of    the cavities forms a thinner portion of the membrane or an opening    leading into this cavity.-   59. The micromechanical device according to any one of items 41 to    58, wherein micromechanical functional elements of the top side,    particularly the trenches mentioned under any one of items 47 to 58,    are not situated, with their edges defining their shape, above    shape-defining edges of micromechanical structures of the bottom    side and micromechanical structures of the top side.-   60. The micromechanical device according to item 59, wherein the    lever length 116 between the starting point of a structure 121    therebelow, particularly of a buried cavity 4, and the starting    point of a structure 119 thereabove, particularly of a trench 6, is    larger than the smaller one of the vertical lever dimensions 118 and    120 (see FIG. 38).-   61. The micromechanical device according to any one of items 44 to    60, wherein, within the body of the micromechanical device,    particularly during production of the device within the wafer    package, at least one cavity is arranged which is connected with the    bottom side or top side of the wafer package by at least one    micromechanical functional element, particularly a tube.-   62. The micromechanical device according to item 61, which can be    used as a pressure differential sensor against a defined referential    pressure or ambient pressure.-   63. The micromechanical device according to item 61 and 62,    comprising at least one microfluidic functional element.-   64. The micromechanical device according to item 63, wherein at    least one microfluidic functional element serves or can serve for    supply of media such as e.g. liquids and gases.-   65. A micromechanical device, wherein at least one microfluidic    functional element according to any one of items 63 to 64 or a    micromechanical functional element according to item 61 has been    produced after performing a process, particularly a CMOS process,    for producing a transistor according to any one of items 1 to 13 or    a circuit according to any one of items 14 to 40.-   66. The micromechanical device according to any one of items 1 to    65, wherein, at least as a partial substrate or substrate, a p-doped    semiconductor material has been used.-   67. The micromechanical device according to any one of items 1 to    65, wherein, at least as a partial substrate or substrate, an    n-doped semiconductor material has been used.-   68. The micromechanical device according to any one of items 44 to    67, wherein, in at least one substrate, a modification of material,    e.g. an SiO₂ layer, is provided which serves as an etching stopper    for the etching of at least one cavity.-   69. The micromechanical device according to any one of items 53 to    68, wherein, in at least one substrate, a modification of material    14 is provided which serves as an etching stopper for the etching of    at least a part of the trenches.-   70. The micromechanical device according to item 69, wherein, in at    least one substrate, at least one modification of material 15 is    provided which acts as a membrane in the region of the trenches.-   71. The micromechanical device according to item 70, wherein at    least one modification of material 15 is made of polysilicon and/or    amorphous silicon and has been deposited on one of the wafers of the    wafer package prior to the wafer bonding.-   72. The micromechanical device according to any one of items 44 to    67 and 69 to 71, wherein at least one cavity has been etched into at    least one substrate in a time-controlled manner.-   73. The micromechanical device according to any one of items 53 to    68 and 70, wherein at least a part of the trenches have been etched    into the substrate in a time-controlled manner.-   74. The micromechanical device according to any one of items 53 to    73, wherein, prior to the etching of the trenches, a semiconductor    process has been performed for producing electrical functional    elements on at least one surface of the wafer package.-   75. The micromechanical device according to item 74, comprising at    least one electrical functional element which has been produced in    the process according to item 74.-   76. The micromechanical device according to item 75, wherein at    least one electrical functional element has the function of an    electrical line or a contact or a through-hole or an electric line    insulator or a resistor or a transistor or a diode or a capacitor or    a coil.-   77. The micromechanical device according to item 76, wherein at    least one of the functional elements is operative to change at least    one parameter—particularly an electrical parameter—in dependence on    mechanical values, particularly tensile stress, compressive stress    and shear stress.-   78. The micromechanical device according to item 77, wherein said    change of parameter can be measured externally of the sensor.-   79. The micromechanical device according to item 77 and 54, wherein    at least one of the functional elements is in a mechanical    functional relationship with at least one web 8,20.-   80. The micromechanical device according to item 77 and 36, wherein    at least one electronic functional element, relative to    -   a) at least one first micromechanical functional element,        particularly a membrane (12 or 21),    -   b) at least two further, second micromechanical functional        elements, particularly trenches (6 or 19), and    -   c) at least one third micromechanical functional element,        particularly a web (8 or 20),    -   said functional elements according to a) to c) being in a        mechanical functional relationship,    -   is positioned on the third micromechanical functional element,        particularly web, in such a manner that said at least one        electronic functional element is situated on or near the point        of highest mechanical stress when the first micromechanical        functional element, particularly a membrane or an inertial mass        (12 or 21) is deformed, particularly deflected.-   81. The micromechanical device according to item 80, wherein at    least one third micromechanical functional element, particularly a    web, is shaped in such a manner that said element has a range of    high homogenized mechanical stress in case of deformation of the    first micromechanical functional element, particularly a membrane or    an inertial mass.-   82. The micromechanical device according to item 81, wherein at    least one electronic functional element is arranged on at least one    such site of high homogenized mechanical stress.-   83. The micromechanical device according to any one of items 41 to    82, wherein at least two wafers have been formed with different    thicknesses.-   84. The micromechanical device according to any one of items 41 to    82, wherein a wafer material is a silicon or SOI material.-   85. The micromechanical device according to any one of items 44 to    79, wherein the cavity is produced in the lowermost wafer prior to    the bonding of three wafers.-   86. The micromechanical device according to item 86, wherein said    three wafers have been produced with different thicknesses.-   87. The micromechanical device according to any one of items 53 to    86, wherein at least one of said second micromechanical functional    elements is a trench (6 or 19) having a non-constant width.-   88. The micromechanical device according to any one of items 54 to    87, wherein at least one web does not divide a trench (6 or 19) but    only extends into it (see e.g. FIG. 25).-   89. The micromechanical device according to any one of items 54 to    88, wherein, between the webs and trenches, a surface is formed on a    membrane which, being suspended on the webs, is quadratic (see e.g.    FIG. 20 or 23), rhombic (see e.g. FIG. 21 or FIG. 22) or round (e.g.    FIG. 24).-   90. The micromechanical device according to item 89, wherein at    least one trench has no bottom and thus is connected to at least one    cavity.-   91. The micromechanical device according to any one of items 41 to    90, which can be used as a pressure sensor and/or acceleration    sensor.-   92. The micromechanical device according to any one of items 41 to    91, comprising symmetrically arranged mechanical first functional    elements, particularly webs, which are connected to at least one    further, second micromechanical functional element, particularly a    membrane or inertial mass, and on which respectively mutually    similar circuit portions of a circuit according to any one of items    14 to 40 are arranged.-   93. The micromechanical device and circuit according to item 92,    wherein the circuit portions arranged on the first micromechanical    functional elements are electrically connected to each other in such    a manner that average values and/or differences will be formed.-   94. The micromechanical device according to any one of items 41 to    93, which at least at a first position comprises a first mechanical    functional element, particularly a web that is mechanically    connected to at least one further, second micromechanical functional    element, particularly a membrane, and has a second position being    without a mechanical function and being subjected to no or only    slight mechanical influence, and wherein, at least at said two    positions, respectively mutually similar circuit portions of a    circuit according to any one of items 14 to 40 are arranged.-   95. The micromechanical device and circuit according to item 94,    wherein the circuit portions arranged at said two positions are    electrically connected to each other in such a manner that average    values and/or differences will be formed.-   96. The micromechanical device and circuit according to any one of    items 92 to 95, wherein the micromechanical device consists of at    least two complete micromechanical partial devices, particularly two    pressure sensors according to any one of items 92 to 95 which again    are in a functional relationship.-   97. The micromechanical device and circuit according to item 96,    wherein, within the circuit, mathematical operations, particularly    the formation of average values and differences, are performed on    electrical output values of said partial devices.-   98. The micromechanical device and circuit according to any one of    items 94 to 97, wherein at least one second circuit portion being    similar to a first circuit portion at said first position,    particularly on a web, is used as a reference, particularly voltage    reference, and is not in a functional relationship with a    micromechanical functional element.-   99. The micromechanical device and circuit according to any one of    items 92 to 98, wherein, to each circuit portion at a first    position, at least one circuit portion similar to the circuit    portion on the respective web, is assigned as a reference, and    wherein said reference is not in a functional relationship with a    micromechanical functional element.-   100. The micromechanical device and circuit according to item 99,    wherein said reference is situated on the neutral fiber.-   101. The micromechanical device and circuit particularly according    to any one of items 92 to 100, wherein a part thereof is formed by    at least one amplifier circuit.-   102. The micromechanical device and circuit particularly according    item 101, wherein said amplifier circuit has a positive and a    negative input.-   103. The micromechanical device and circuit according to any one of    items 1 to 101, which in wide regions is provided with a protection    against humidity and/or in- and out-diffusion of protons.-   104. The micromechanical device and circuit according to item 103,    wherein said diffusion protection consists of a silicon-nitride    layer.

Further advantages of the invention are:

-   1. Reduction of the number of required wafer bond connections-   2. Reduction of parasitic elements    -   a) Elimination of sources of mechanical stress    -   b) Protection against dissipation of unavoidable mechanical        stress    -   c) Maximization, homogenization and linearization of mechanical        useful stress fields    -   d) Reduction of the dissipation of electronic components    -   e) Reduction of the dissipation of electronic circuits    -   f) Reduction of the dissipation of micromechanical functional        elements-   3. Increasing the tolerance of the construction towards mechanical    and electrical manufacturing variations-   4. Reduction of the effects of unavoidable parasitic elements-   5. Reduction of the influence of the design and connection    technology-   6. Flexibilization of the use of sensors on the side of the user-   7. Reduction of the required die area-   8. Possibility of coupling to high-volume standard CMOS lines,    particularly such lines with p-doped substrates

These properties are realized particularly by the measures describedhereunder, which can be applied individually or in total or partialcombination:

-   1. Reduction of the number of required wafer bond connections by    -   a) Producing cavities prior to the CMOS processing-   2. Reduction of parasitic elements by    -   a) Elimination of sources of mechanical stress, particularly by        -   i) Avoidance of unnecessary layers on the micromechanical            functional elements, particularly on pressure sensor            membranes    -   b) Protection against dissipation of unavoidable mechanical        stress, particularly by        -   i) Containment of the stress by mechanical guard rings, and        -   ii) Reduction of the depth of cavities in the material,            wherein the latter has a higher areal moment of inertia    -   c) Maximization, homogenization and linearization of useful        stress fields, particularly by        -   i) Etching trenches into pressure membranes        -   ii) Selection of the trench shape        -   iii) Distance between rear-side structures and buried            structures on the one hand and front-side structures on the            other hand for reduction of adjustment errors    -   d) Reduction of the dissipation of electronic components by        -   i) Use of self-adjusting structures    -   e) Reduction of the dissipation of electronic circuits by        -   i) Use of a compact, symmetrical, self-adjusting special            transistor        -   ii) Use of a compact, symmetrical, self-adjusting            differential amplifier stage        -   iii) Use of a compact, self-adjusting, symmetrical active            Wheatstone bridge    -   f) Reduction of the dissipation of micromechanical functional        elements by        -   i) Use of defined, CMOS-compatible etching stops        -   ii) Use of particularly miniaturized special transistors-   3. Increasing the tolerance of the construction towards mechanical    and electrical manufacturing variations    -   a) Differentiation of the stress direction    -   b) Differentiation between stressed and unstressed circuit        portions    -   c) Differentiation between circuit portions at different        symmetry positions    -   d) Suitable compensatory connection of circuit portions which        can detect the differences i to iii by measuring    -   e) Use of particularly miniaturized special transistors    -   f) Miniaturization of the mechanical design by well-aimed        reduction of the layer stack in the region of micromechanical        functional elements-   4. Reduction of the effects of unavoidable parasitic elements    -   a) Compensatory circuits    -   b) Use of particularly miniaturized special transistors-   5. Reduction of the influence of the design and connection    technology by    -   a) Reduction of the depth of cavities in the material, whereby        the material has a higher areal moment of inertia    -   b) Use of round cavities, whereby the vertical areal moment of        inertia is enlarged-   6. Flexibilization of the use of sensors on the side of the user by    -   a) Adjustability of the amplification by the user-   7. Reduction of the required die area    -   a) Reduction of the depth of cavities in the material, whereby        the material has a higher areal moment of inertia and the sensor        can be reduced in size without loss of stability    -   b) Use of particularly miniaturized special transistors    -   c) Forming a minimal access opening for gases and liquids        leading to a buried cavity-   8. Possibility of coupling to high-volume standard CMOS lines,    particularly such lines with p-doped substrates    -   a) Forming the cavities with defined etching stopper prior to        the CMOS process    -   b) Production of micromechanical functional elements on the        surface, such as trenches, after the CMOS processing, by means        of plasma or DRIE etching    -   c) Forming minimal access openings leading to buried cavities,        after the CMOS processing.

LIST OF REFERENCE NUMERALS

-   1. First wafer-   2. Oxide layer-   3. Straight wall of cavity 4-   4 Cavity 4-   5 Second wafer-   6 Trenches in the wafer package-   7 Thin membrane regions defined by trenches 6 and cavity 4-   8 Webs interrupting the trenches 6-   8 a Bending element-   9 Components for detecting the mechanical stress-   10 Terminals with terminal lines-   11 Surface of the wafer package-   12 Central plate of the membrane-   13 First wafer-   14 SiO₂ layer-   15 Polysilicon layer-   16 Second layer-   17 Second oxide layer-   18 Cavity-   19 Trenches-   20 Webs interrupting the trenches-   21 Central plate of the membrane-   22 Components for detecting the mechanical stress-   23 Terminals with terminal lines-   24 Surface of the wafer package-   25 Membrane of small thickness-   26 Negative terminal of the Wheatstone bridge-   27 Positive terminal of the Wheatstone bridge-   28 First clamp for capturing the voltage on the Wheatstone bridge-   29 Lower p-channel MOS diode of the reference voltage source for the    Wheatstone bridge-   30 Upper p-channel MOS diode of the reference voltage source for the    Wheatstone bridge-   31 First p-channel MOS transistor of the Wheatstone bridge-   32 Second p-channel MOS transistor of the Wheatstone bridge-   33 Third p-channel MOS transistor of the Wheatstone bridge-   34 Fourth p-channel MOS transistor of the Wheatstone bridge-   35 Reference voltage line-   36 Second clamp for capturing the voltage on the Wheatstone bridge-   37 n+-channel stopper implant-   38 Gate-connector transistor 32 and 34 in low-impedance polysilicon-   39 Gate-connector transistor 33 and 31 in low-impedance polysilicon-   40 n−-doped surface (non-conducting)-   41 Upper structure sensitive to mechanical stress, e.g. a Wheatstone    bridge according to FIG. 12-   42 Right-hand structure sensitive to mechanical stress, e.g. a    Wheatstone bridge according to FIG. 12-   43 Lower structure sensitive to mechanical stress, e.g. a Wheatstone    bridge according to FIG. 12-   44 First differential amplifier p-channel transistor-   45 Second differential amplifier p-channel transistor-   46 Third differential amplifier p-channel transistor-   47 Fourth differential amplifier p-channel transistor-   48 Reference voltage for transistors 44,45,46,47-   49 Current-source feed line for transistors 44,45,46,47-   50 Common drain contact of the p-channel transistors 44,45,46,47-   51 Connector transistor 46, negative output knot of the differential    amplifier-   52 Connector transistor 45, positive output knot of the differential    amplifier-   53 Connector transistor 44, negative output knot of the differential    amplifier-   54 Connector transistor 47, positive output knot of the differential    amplifier-   55 Third p-channel transistor for reference bridge circuit-   56 Fourth p-channel transistor for reference bridge circuit-   57 Upper structure sensitive to mechanical stress, e.g. a Wheatstone    bridge according to FIG. 12 as a reference structure for 41 in the    region free of mechanical stress-   58 Right-hand structure sensitive to mechanical stress, e.g. a    Wheatstone bridge according to FIG. 12 as a reference structure for    42 in the region free of mechanical stress-   59 Lower structure sensitive to mechanical stress, e.g. a Wheatstone    bridge according to FIG. 12 as a reference structure for 43 in the    region free of mechanical stress-   60 Left-hand structure sensitive to mechanical stress, e.g. a    Wheatstone bridge according to FIG. 12 as a reference structure for    44 in the region free of mechanical stress-   61 Differential amplifier: current mirror transistor corresponding    to transistor 69-   62 Differential amplifier: current mirror transistor corresponding    to transistor 70-   63 Differential amplifier: current mirror transistor corresponding    to transistor 71-   64 Differential amplifier: current mirror transistor corresponding    to transistor 72-   65 Reference amplifier: first differential amplifier p-channel    transistor-   66 Reference amplifier: second differential amplifier p-channel    transistor-   67 Reference amplifier: third differential amplifier p-channel    transistor-   68 Reference amplifier: fourth differential amplifier p-channel    transistor-   69 Reference amplifier: current mirror transistor corresponding to    transistor 61-   70 Reference amplifier: current mirror transistor corresponding to    transistor 62-   71 Reference amplifier: current mirror transistor corresponding to    transistor 63-   72 Reference amplifier: current mirror transistor corresponding to    transistor 64-   73 Reference amplifier: n-channel current source transistor (current    mirror)-   74 Reference amplifier: n-channel current source transistor (current    mirror)-   75 Negative terminal-   76 Positive terminal-   77 Negative output signal-   78 Positive output signal-   78 a Active region pan-   79 p+-contact implant (source region)-   79 a Metal line-   80 p+-contact implant (drain region)-   80 a Metal line-   81 Poly gate of a self-adjusting p-channel transistor-   81 a Gate oxide-   82 n+-implant region (channel stop)-   83 n+-implant region (channel stop)-   84 Feed line of highly doped polysilicon-   85 First p-channel MOS transistor of the Wheatstone bridge-   86 Second p-channel MOS transistor of the Wheatstone bridge-   87 Third p-channel MOS transistor of the Wheatstone bridge-   88 Fourth p-channel MOS transistor of the Wheatstone bridge-   89 Left-hand tap-   90 Right-hand tap-   91 Negative pole-   92 Positive pole-   93 Second group of trenches for decoupling the membrane from the die    body-   94 Webs interrupting the group of second trenches 93-   95 Third group of trenches for further decoupling the membrane from    the die body-   96 Webs interrupting the third group of second trenches 95-   97 Boss with grid structure (support structure)-   98 Bore in the cavity for differential pressure sensors-   99 Mechanical guard ring for prevention of dissipation of the    mechanical stress introduced by the bond system-   100 Left-hand structure sensitive to mechanical stress, e.g. a    Wheatstone bridge according to FIG. 12-   101 One-transistor element-   102 Negative terminal-   103 Positive terminal-   104 Upper transistor left-hand side (p-channel)-   105 Upper transistor right-hand side (p-channel)-   106 Lower transistor left-hand side (p-channel)-   107 Lower transistor right-hand side (p-channel)-   108 Upper reference transistor (p-channel)-   109 Lower reference transistor (p-channel)-   110 Internal reference voltage-   111 First output-   112 Second output-   113 Parasitic first transistor-   114 Parasitic second transistor-   115 Entire transistor field plate-   116 Lever length (here, the example of the cavity wall 3 to the    trench wall)-   117 Example: trench wall-   118 Height of upper structure (here, by way of example, depth of    trench 6)-   119 Receptor point of the upper structure (here, by way of example,    depth of trench 6)-   120 Height of lower structure (here, by way of example, depth of    cavity 4)-   121 Receptor point of the lower structure (here, by way of example,    cavity 4)

1. A micro-electromechanical semiconductor component comprising: a firstsemiconductor substrate having an upper face, a second semiconductorsubstrate having an upper face, both semiconductor substrates beingbonded resting on the upper faces thereof, a cavity being introducedinto the upper face of at least one of the two semiconductor substrates,and the cavity being defined by lateral walls and opposing top andbottom walls which are formed by the two semiconductor substrates, andone of the top or the bottom wall acting as a reversibly deformablemembrane, and an opening extending through the respective semiconductorsubstrate being arranged in the other of the top or the bottom wall ofthe cavity.
 2. The micro-electromechanical semiconductor componentaccording to claim 1, characterized in that, an insulating layer,particularly an oxide layer, is arranged on the top face of at least oneof the two semiconductor substrates.
 3. The micro-electromechanicalsemiconductor component according to claim 1, characterized in thatelectrical and/or electronic components are formed on and/or in themembrane and/or on and/or in one of the two semiconductor substrates. 4.A method for producing a micro-electromechanical semiconductorcomponent, comprising the following steps: providing a firstsemiconductor substrate having an upper face, providing a secondsemiconductor substrate having an upper face, forming a cavity in theupper face of at least one of the two semiconductor substrates, bondingthe two semiconductor substrates resting on each other by their upperfaces, etching, into one of the two semiconductor substrates, an openingentering the cavity.
 5. The method according to claim 4, furthercomprising forming at least one of electrical or electronic componentsat least one of in or on at least one of the two semiconductorsubstrates (1,5), prior to etching the opening entering the cavity. 6.The method according to claim 4, further comprising forming a region ofthe other of the two semiconductor substrates opposite to the openingentering the cavity, as a reversibly deformable membrane by generatingdepressions that locally thin a material thickness of the region.